1. Field of the Invention
The present invention relates to a method for verifying the accuracy of bit-map memory test programs, especially a method that employs a Focused Ion Beam (FIB) apparatus to make or break connections of one or more word lines or bit lines of a physical memory. The FIB modeling result is then compared with that from the bit-map memory test program to verify whether the bit-map memory test program is reliable.
2. Description of Related Art
Each step in a memory manufacturing process has to undergo stringent quality control to produce a high and stable yield rate. When the yield rate drops below a normal standard, test engineers are called in to investigate the cause. Bit-map memory test programs are one of the more commonly used programs to test physical memory. The testing parameters for the bit-map memory test program first have to be setup according to the physical address table provided by the memory manufacturer. The data output pattern from the memory test program is regarded as the electrical address, which is supposed to match the corresponding physical address in the physical memory. The output of the bit-map memory test program displayed on a screen is represented by a stream of 0's and 1's in a specific pattern.
During bit-map memory testing, test data is first written into the physical memory, and then the data is read out of memory. If the tested memory is a good memory chip, the results of the test program should correspond to the test data written into specified memory locations. If faulty memory addresses or memory cells exist in the physical memory, the data values at those memory locations cannot be read, causing the corresponding data image to be different from the data input into the memory. Through such comparison of FIB modeling results and the bit-map memory test results, whether or not the bit-map memory test detects all faulty memory address lines and data cells in a memory chip can thus be verified.
It is absolutely important that the physical memory address table provided by the memory manufacturer be a complete match with the physical memory address. Only then, can the memory test program based on the physical memory address table be successfully performed on the physical memory with high accuracy. With reference to FIG. 2 to FIG. 4, current memory architecture allows physical memory addresses to be arranged in one of several ways. With reference to FIG. 2, the memory address can be arranged sequentially from left to right. With reference to FIG. 3, the data sequence can start at the center and extend to one side. When the data stream reaches the end of the line, the data sequence restarts from the center of the same line but extends in the opposite direction. With reference to FIG. 4, data can be alternately arranged from left to right the first time through, and then it is started again on the same line from left to right but in every other slot until the end of the line.
It only takes a small data discrepancy in the physical memory to render the tested memory useless, because the test program is unable to test all physical memories to produce a clean test report. To prevent such errors during memory testing with the bit-map memory test program, a verification process is developed in the present invention by means of Focused Ion Beam (FIB) apparatus, which can tell how accurate and reliable a bit-map memory test program is.